Microelectromechanical (MEM) fabrication technologies such as surface and bulk micromachining and LIGA (an acronym based on the first letters for the German words for lithography, electroplating and injection molding) have been extensively developed in recent years to form many different types of microsystems and microsensors. For certain uses, these Microsystems and microsensors would benefit considerably from a long-life internal power supply. For example, microsensors or microsystems placed inside medical implantable devices or used for unattended structural monitoring often are not easily accessible so that batteries cannot be replaced without substantial expense or damage. In the case of an implantable medical device, such as a heart pacemaker implanted within a patient, the replacement of a battery generally requires that an operation be performed at some risk to the patient, and that the entire medical device be replaced at a cost of up to several tens of thousands of dollars. What is needed is a miniature power source which harvests ambient energy to generate electrical power on a sustainable basis.
Previous sources of electrical power based on harvesting mechanical energy have met with limited success due to the small amount of electrical power generated, the low voltage produced, the large size of the device, or a combination of these factors. The present invention represents an advance over the prior art in providing a microelectromechanical (MEM) apparatus which can be used as an electrical power generator, or alternately as a vibration sensor, or as an acceleration or impact sensor. The MEM apparatus of the present invention utilizes a plurality of permanent magnets, which are spaced apart and arranged side-by-side to produce a relatively rapid change in magnetic flux over a small range of displacement, in combination with a meandering (i.e. serpentine) electrical pickup which additively senses the magnetic flux from each of the permanent magnets to generate a relatively large voltage and a relatively large amount of electrical power from a small-sized device.
An advantage of the MEM apparatus of the present invention is that it can be sized, as needed, to produce a predetermined level of electrical power of up to a few milliwatts or more.
Another advantage is that the MEM apparatus of the present invention can be fabricated using conventional micromachining technology so that piece-part assembly can be minimized.
A further advantage of the MEM apparatus of the present invention is that it can be integrated directly on a common substrate with various types of microsystems, microsensors or integrated circuitry to provide electrical power to these devices, or to sense vibration, acceleration or impact.
These and other advantages of the present invention will become evident to those skilled in the art.